df: dereference symlinks to disk device nodes

This is so the matching for the device is done on the canonical name
of the disk node, rather than on the path of the symlink.
In any case the user will generally want to use the symlink target.

* src/df.c (get_disk): Canonicalize the passed file,
before matching against the list of mounted file system devices.
Note we pass the original symlink name to the "file" output field,
as the symlink target is usually available through the "source" field.
* tests/df/df-symlink.sh: Test the dereferencing operation.
* tests/local.mk: Mention the new test.
* NEWS: Mention the fix.
Reported by Ondrej Oprala

4 files changed, 44 insertions, 1 deletions

diff --git a/NEWS b/NEWS
index b9678859c..9274645a3 100644
--- a/NEWS
+++ b/NEWS
@@ -8,6 +8,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   mount points.  Previously it may have failed to output some mount points.
   [bug introduced in coreutils-8.21]
 
+  df now processes symbolic links to disk device nodes correctly.  Previously
+  df displayed the symlink's device rather than that for the device node.
+  [This bug was present in "the beginning".]
+
   install now removes the target file if the strip program failed for any
   reason.  Before, that file was left behind, sometimes even with wrong
   permissions.
diff --git a/src/df.c b/src/df.c
index ba8ef15c8..8eabcbbaa 100644
--- a/src/df.c
+++ b/src/df.c
@@ -1056,6 +1056,11 @@ get_disk (char const *disk)
 {
   struct mount_entry const *me;
   struct mount_entry const *best_match = NULL;
+  char const *file = disk;
+
+  char *resolved = canonicalize_file_name (disk);
+  if (resolved && resolved[0] == '/')
+    disk = resolved;
 
   for (me = mount_list; me; me = me->me_next)
     {
@@ -1063,9 +1068,11 @@ get_disk (char const *disk)
         best_match = me;
     }
 
+  free (resolved);
+
   if (best_match)
     {
-      get_dev (best_match->me_devname, best_match->me_mountdir, disk, NULL,
+      get_dev (best_match->me_devname, best_match->me_mountdir, file, NULL,
                best_match->me_type, best_match->me_dummy,
                best_match->me_remote, NULL, false);
       return true;
diff --git a/tests/df/df-symlink.sh b/tests/df/df-symlink.sh
new file mode 100755
index 000000000..45acfaa29
--- /dev/null
+++ b/tests/df/df-symlink.sh
@@ -0,0 +1,31 @@
+#!/bin/sh
+# Ensure that df dereferences symlinks to disk nodes
+
+# Copyright (C) 2013 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ df
+
+disk=$(df --out=source '.' | tail -n1) ||
+  skip_ "cannot determine '.' file system"
+
+ln -s "$disk" symlink || framework_failure_
+
+df --out=source,target "$disk" > exp || skip_ "cannot get info for $disk"
+df --out=source,target symlink > out || fail=1
+compare exp out || fail=1
+
+Exit $fail
diff --git a/tests/local.mk b/tests/local.mk
index 9b851f434..9a54e7b07 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -460,6 +460,7 @@ all_tests =					\
   tests/df/header.sh				\
   tests/df/df-P.sh				\
   tests/df/df-output.sh				\
+  tests/df/df-symlink.sh			\
   tests/df/unreadable.sh			\
   tests/df/total-unprocessed.sh			\
   tests/df/no-mtab-status.sh			\